Municipal sewer lines extend from homes, civic facilities and commercial buildings to sewage treatment facilities. The lines have a maximum fluid capacity that exceeds the actual flow leaving space filled with air and other gasses.
Gravity induces flow of fluids and solids in sewer lines. To maintain adequate flow the lines generally have a uniform slope from an inlet pipe end down to an outlet pipe end and no raised areas in the pipe that would hold liquids or solids. The sewer lines are preferably sufficiently deep to receive sewage from basements without the use of sewage pumps.
Potable water lines may be above sewer lines. The water is under pressure and is substantially free of air. However it is desirable for lines to be at controlled elevations to avoid potential problems. These problems include freezing in cold periods, heat expansion in hot periods, and a collection of solids in a low area of a pipe. The collected solids are generally inert sand or scale from the aquifer or water supply pumps and pipes, that are not moved by water flow through the line pipes. The ground surface above sewer lines varies substantially from flat and horizontal in most environments.
An operator sitting in the operator's seat on one side of a boom of a prior art hydraulic excavator can see the bucket on the end of an excavator stick when the bucket first enters a trench. After the bucket moves down into a trench, that is being dug, several feet the operator can only see the bucket by moving his head to a position against a side window and looking along one side of the boom and the stick. The side window is not openable because it is close to the boom and the boom moves relative to the operator's station. As the depth of a trench increases, the portion of a bucket that can be seen from the operator's station decreases. A decreased width of a trench also decrease the operators view of the bucket and the bottom of the trench.
An operator tends to become fatigued in less time when a side of his head is tilted to one side and in contact with an operator's compartment wall.
Trenches are often over twenty five feet deep. With deep trenches there is a possibility of a wall collapse. To protect individuals working in the trench, steel revetment is used. These structures have steel walls connected together near their top edges by two cross beams. With a deep trench an upper revetment structure may sit on top of a lower revetment structure. These revetment structures are referred to as boxes. The walls are normally eight feet high and twenty four feet long. The total weight of one unit is as much as six tons. A light load for an excavator but requires a long reach from the excavator. A box may be anchored if there is a wall collapse. Additional force is required to lift a box from a trench after a wall collapse. Due to their limited height several of the boxes may be stacked together in a trench section that is more than thirty feet deep.
One excavator with a long reach boom that can form a trench which is more than twenty feet deep has a weight of about 112,000 pounds and a 12.5 liter displacement engine. A somewhat larger machine may be required to form a trench that is thirty feet deep at an acceptable rate. Smaller excavators are employed to form a thirty foot deep trench by digging a trench with a width that exceeds the width of the excavator and a depth of five feet or more and then digging a narrow trench that provides the required depth. This two step procedure requires the movement of substantially more material. The two step procedure increases the cost of installing a pipe at the required depth.